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Superman might be able to hear a clock ticking 200 metres away, but life would be hell for mere mortals if we had that kind of ability, says Dr Bill Budd.

Hearing isn't like other senses; if a light is too bright we can always close our eyes or turn away, but our hearing is always 'on', even when we are asleep, and super-sensitivity would be quite impairing, says Budd, a lecturer and scientist at the University of Newcastle.

"We would be surrounded by such a cacophony of sound we wouldn't hear anything very well."

Some people, however, are more sensitive to particular aspects of sound.

"We do have people we refer to as 'golden ears'," he says, "people who have much better hearing than others, but they can be very sensitive to some aspects of sound but not necessarily to others.

"Golden ears may be able to hear very, very soft sounds, or sounds at high frequencies, or may be able to detect minute timing differences in how sounds arrive at each ear, but we don't often see people who have above average ability on all those aspects of hearing. You can be good at some and not others."

"Hearing is very complex. It's not a matter of having a whole bunch of people who hear normally and then some people who have super hearing. We come across a rich tapestry of hearing abilities."

Sound frequencies

Sounds are what we hear when something causes air to vibrate. The human ear can hear air vibrations as sound if they vibrate at frequencies between 20 and 20,000 hertz.

"To put that in perspective a dog can hear up to 45,000, a cat up to 65,000 hertz." Someone who can hear at 20,000 hertz is referred to in the research world as a 'dog'. The rest of us are likely to be somewhere between 10,000 and 15,000 … and declining," says Budd.

In fact, the closest we get to 'super-hearing' is at birth.

"That's when the peripheral nervous system, the ear and the cochlea, (the spiral-shaped cavity in the inner ear) are in the best shape that they're ever going to be in your whole life. However our ears only play part of the role in hearing, most of the really complex work is actually done by the brain."

For this reason our basic hearing ability isn't developed until sometime between the ages of 5 and 10 years when auditory brain areas become fully developed.

Depending on our exposure to noise hearing sensitivity can start to decline in our twenties. "From thirty it can be a slippery slope down to hearing impairment", he says.

Sensitive structures

It's the amazing sensitivity of our ear structures that doom them to early decline, he says.

The softest sound we can hear corresponds to air vibration as small as one tenth the diameter of an atom. Our brain can automatically detect differences in sound on the order of 10 millionths of a second.

"We all posses this extraordinary sensitivity, so in one sense we ALL have 'super hearing'," says Budd.

"But the bad news is that the physiology mechanisms that give us this amazing ability are very fragile, so loud noise exposure, or certain types of brief loud sounds, like explosions, can irreversibly damage those inner hair cells of the ear.

"Once they're damaged they don't regenerate and that's why you have general decay of hearing as you get older."

In the increasingly noisy age of the iPod, the message emerging from hearing research is to regularly give the ears a rest.

"One area being actively looked at is whether you get hearing damage from not just intensity of sound but sound dose. The ear can tolerate quite loud sound, for example 90 decibels for a few minutes without adverse effect, but you couldn't listen to the same sounds for more than five hours a week without risking permanent damage."

Dr Bill Budd is a lecturer in psychology at the University of Newcastle. He specialises in neuroimaging and auditory processing. He spoke to Annie Hastwell.